NEWS

new material on paths, etc. Also rationalisation

Isabelle NEWS -- history of user-relevant changes
=================================================

(Note: Isabelle/jEdit shows a tree-view of the NEWS file in Sidekick.)


New in this Isabelle version
----------------------------

*** General ***

* Embedded content (e.g. the inner syntax of types, terms, props) may be
delimited uniformly via cartouches. This works better than old-fashioned
quotes when sub-languages are nested.

* Type-inference improves sorts of newly introduced type variables for
the object-logic, using its base sort (i.e. HOL.type for Isabelle/HOL).
Thus terms like "f x" or "\<And>x. P x" without any further syntactic context
produce x::'a::type in HOL instead of x::'a::{} in Pure. Rare
INCOMPATIBILITY, need to provide explicit type constraints for Pure
types where this is really intended.

* Simplified outer syntax: uniform category "name" includes long
identifiers. Former "xname" / "nameref" / "name reference" has been
discontinued.

* Mixfix annotations support general block properties, with syntax
"(\<open>x=a y=b z \<dots>\<close>". Notable property names are "indent", "consistent",
"unbreakable", "markup". The existing notation "(DIGITS" is equivalent
to "(\<open>indent=DIGITS\<close>". The former notation "(00" for unbreakable blocks
is superseded by "(\<open>unbreabable\<close>" --- rare INCOMPATIBILITY.

* Mixfix annotations support delimiters like \<^control>\<open>cartouche\<close> --
this allows special forms of document output.

* Raw LaTeX output now works via \<^latex>\<open>...\<close> instead of raw control
symbol \<^raw:...>. INCOMPATIBILITY, notably for LaTeXsugar.thy and its
derivatives.

* \<^raw:...> symbols are no longer supported.

* New symbol \<circle>, e.g. for temporal operator.

* Old 'header' command is no longer supported (legacy since
Isabelle2015).

* Command 'bundle' provides a local theory target to define a bundle
from the body of specification commands (such as 'declare',
'declaration', 'notation', 'lemmas', 'lemma'). For example:

bundle foo
begin
  declare a [simp]
  declare b [intro]
end

* Command 'unbundle' is like 'include', but works within a local theory
context. Unlike "context includes ... begin", the effect of 'unbundle'
on the target context persists, until different declarations are given.

* Splitter in simp, auto and friends:
- The syntax "split add" has been discontinued, use plain "split".
- For situations with many conditional or case expressions,
there is an alternative splitting strategy that can be much faster.
It is selected by writing "split!" instead of "split". It applies
safe introduction and elimination rules after each split rule.
As a result the subgoal may be split into several subgoals.

* Proof method "blast" is more robust wrt. corner cases of Pure
statements without object-logic judgment.

* Pure provides basic versions of proof methods "simp" and "simp_all"
that only know about meta-equality (==). Potential INCOMPATIBILITY in
theory imports that merge Pure with e.g. Main of Isabelle/HOL: the order
is relevant to avoid confusion of Pure.simp vs. HOL.simp.

* Commands 'prf' and 'full_prf' are somewhat more informative (again):
proof terms are reconstructed and cleaned from administrative thm
nodes.

* The command 'unfolding' and proof method "unfold" include a second
stage where given equations are passed through the attribute "abs_def"
before rewriting. This ensures that definitions are fully expanded,
regardless of the actual parameters that are provided. Rare
INCOMPATIBILITY in some corner cases: use proof method (simp only:)
instead, or declare [[unfold_abs_def = false]] in the proof context.


*** Prover IDE -- Isabelle/Scala/jEdit ***

* Dockable window "Symbols" also provides access to 'abbrevs' from the
outer syntax of the current theory buffer. This provides clickable
syntax templates, including entries with empty abbrevs name (which are
inaccessible via keyboard completion).

* Cartouche abbreviations work both for " and ` to accomodate typical
situations where old ASCII notation may be updated.

* Isabelle/ML and Standard ML files are presented in Sidekick with the
tree structure of section headings: this special comment format is
described in "implementation" chapter 0, e.g. (*** section ***).

* IDE support for the Isabelle/Pure bootstrap process, with the
following independent stages:

  src/Pure/ROOT0.ML
  src/Pure/ROOT.ML
  src/Pure/Pure.thy
  src/Pure/ML_Bootstrap.thy

The ML ROOT files act like quasi-theories in the context of theory
ML_Bootstrap: this allows continuous checking of all loaded ML files.
The theory files are presented with a modified header to import Pure
from the running Isabelle instance. Results from changed versions of
each stage are *not* propagated to the next stage, and isolated from the
actual Isabelle/Pure that runs the IDE itself. The sequential
dependencies of the above files are only observed for batch build.

* Highlighting of entity def/ref positions wrt. cursor.

* Refined folding mode "isabelle" based on Isar syntax: 'next' and 'qed'
are treated as delimiters for fold structure; 'begin' and 'end'
structure of theory specifications is treated as well.

* Sidekick parser "isabelle-context" shows nesting of context blocks
according to 'begin' and 'end' structure.

* Syntactic indentation according to Isabelle outer syntax. Action
"indent-lines" (shortcut C+i) indents the current line according to
command keywords and some command substructure. Action
"isabelle.newline" (shortcut ENTER) indents the old and the new line
according to command keywords only; see also option
"jedit_indent_newline".

* Semantic indentation for unstructured proof scripts ('apply' etc.) via
number of subgoals. This requires information of ongoing document
processing and may thus lag behind, when the user is editing too
quickly; see also option "jedit_script_indent" and
"jedit_script_indent_limit".

* Action "isabelle.select-entity" (shortcut CS+ENTER) selects all
occurences of the formal entity at the caret position. This facilitates
systematic renaming.

* Action "isabelle.keymap-merge" asks the user to resolve pending
Isabelle keymap changes that are in conflict with the current jEdit
keymap; non-conflicting changes are always applied implicitly. This
action is automatically invoked on Isabelle/jEdit startup and thus
increases chances that users see new keyboard shortcuts when re-using
old keymaps.

* Document markup works across multiple Isar commands, e.g. the results
established at the end of a proof are properly identified in the theorem
statement.

* Command 'proof' provides information about proof outline with cases,
e.g. for proof methods "cases", "induct", "goal_cases".

* Completion templates for commands involving "begin ... end" blocks,
e.g. 'context', 'notepad'.

* Additional abbreviations for syntactic completion may be specified
within the theory header as 'abbrevs'. The theory syntax for 'keywords'
has been simplified accordingly: optional abbrevs need to go into the
new 'abbrevs' section.

* Global abbreviations via $ISABELLE_HOME/etc/abbrevs and
$ISABELLE_HOME_USER/etc/abbrevs are no longer supported. Minor
INCOMPATIBILITY, use 'abbrevs' within theory header instead.

* ML and document antiquotations for file-systems paths are more uniform
and diverse:

  @{path NAME}   -- no file-system check
  @{file NAME}   -- check for plain file
  @{dir NAME}    -- check for directory

Minor INCOMPATIBILITY, former uses of @{file} and @{file_unchecked} may
have to be changed.


*** Isar ***

* The defining position of a literal fact \<open>prop\<close> is maintained more
carefully, and made accessible as hyperlink in the Prover IDE.

* Commands 'finally' and 'ultimately' used to expose the result as
literal fact: this accidental behaviour has been discontinued. Rare
INCOMPATIBILITY, use more explicit means to refer to facts in Isar.

* Command 'axiomatization' has become more restrictive to correspond
better to internal axioms as singleton facts with mandatory name. Minor
INCOMPATIBILITY.

* Many specification elements support structured statements with 'if' /
'for' eigen-context, e.g. 'axiomatization', 'abbreviation',
'definition', 'inductive', 'function'.

* Toplevel theorem statements support eigen-context notation with 'if' /
'for' (in postfix), which corresponds to 'assumes' / 'fixes' in the
traditional long statement form (in prefix). Local premises are called
"that" or "assms", respectively. Empty premises are *not* bound in the
context: INCOMPATIBILITY.

* Command 'define' introduces a local (non-polymorphic) definition, with
optional abstraction over local parameters. The syntax resembles
'definition' and 'obtain'. It fits better into the Isar language than
old 'def', which is now a legacy feature.

* Command 'obtain' supports structured statements with 'if' / 'for'
context.

* Command '\<proof>' is an alias for 'sorry', with different
typesetting. E.g. to produce proof holes in examples and documentation.

* The old proof method "default" has been removed (legacy since
Isabelle2016). INCOMPATIBILITY, use "standard" instead.

* Proof methods may refer to the main facts via the dynamic fact
"method_facts". This is particularly useful for Eisbach method
definitions.

* Proof method "use" allows to modify the main facts of a given method
expression, e.g.

  (use facts in simp)
  (use facts in \<open>simp add: ...\<close>)


*** Pure ***

* Code generator: config option "code_timing" triggers measurements of
different phases of code generation. See src/HOL/ex/Code_Timing.thy for
examples.

* Code generator: implicits in Scala (stemming from type class instances)
are generated into companion object of corresponding type class, to resolve
some situations where ambiguities may occur.


*** HOL ***

* New proof method "argo" using the built-in Argo solver based on SMT technology.
The method can be used to prove goals of quantifier-free propositional logic,
goals based on a combination of quantifier-free propositional logic with equality,
and goals based on a combination of quantifier-free propositional logic with
linear real arithmetic including min/max/abs. See HOL/ex/Argo_Examples.thy for
examples.

* Type class "div" with operation "mod" renamed to type class "modulo" with
operation "modulo", analogously to type class "divide".  This eliminates the
need to qualify any of those names in the presence of infix "mod" syntax.
INCOMPATIBILITY.

* The unique existence quantifier no longer provides 'binder' syntax,
but uses syntax translations (as for bounded unique existence). Thus
iterated quantification \<exists>!x y. P x y with its slightly confusing
sequential meaning \<exists>!x. \<exists>!y. P x y is no longer possible. Instead,
pattern abstraction admits simultaneous unique existence \<exists>!(x, y). P x y
(analogous to existing notation \<exists>!(x, y)\<in>A. P x y). Potential
INCOMPATIBILITY in rare situations.

* Renamed session HOL-Multivariate_Analysis to HOL-Analysis.

* Moved measure theory from HOL-Probability to HOL-Analysis. When importing
HOL-Analysis some theorems need additional name spaces prefixes due to name
clashes.
INCOMPATIBILITY.

* In HOL-Probability the type of emeasure and nn_integral was changed
from ereal to ennreal:
  emeasure :: 'a measure => 'a set => ennreal
  nn_integral :: 'a measure => ('a => ennreal) => ennreal
INCOMPATIBILITY.

* HOL-Analysis: more complex analysis including Cauchy's inequality, Liouville theorem,
open mapping theorem, maximum modulus principle, Residue theorem, Schwarz Lemma.

* HOL-Analysis: Theory of polyhedra: faces, extreme points, polytopes, and the Krein–Milman
Minkowski theorem.

* HOL-Analysis: Numerous results ported from the HOL Light libraries: homeomorphisms,
continuous function extensions and other advanced topics in topology

* Number_Theory: algebraic foundation for primes: Generalisation of
predicate "prime" and introduction of predicates "prime_elem",
"irreducible", a "prime_factorization" function, and the "factorial_ring"
typeclass with instance proofs for nat, int, poly. Some theorems now have
different names, most notably "prime_def" is now "prime_nat_iff".
INCOMPATIBILITY.

* Probability: Code generation and QuickCheck for Probability Mass
Functions.

* Theory Set_Interval.thy: substantial new theorems on indexed sums
and products.

* Theory List.thy:
  listsum ~> sum_list
  listprod ~> prod_list

* Theory Library/LaTeXsugar.thy: New style "dummy_pats" for displaying
equations in functional programming style: variables present on the
left-hand but not on the righ-hand side are replaced by underscores.

* "surj" is a mere input abbreviation, to avoid hiding an equation in
term output.  Minor INCOMPATIBILITY.

* Theory Library/Combinator_PER.thy: combinator to build partial
equivalence relations from a predicate and an equivalence relation.

* Theory Library/Perm.thy: basic facts about almost everywhere fix
bijections.

* Theory Library/Normalized_Fraction.thy: allows viewing an element
of a field of fractions as a normalized fraction (i.e. a pair of
numerator and denominator such that the two are coprime and the
denominator is normalized w.r.t. unit factors)

* Locale bijection establishes convenient default simp rules
like "inv f (f a) = a" for total bijections.

* Former locale lifting_syntax is now a bundle, which is easier to
include in a local context or theorem statement, e.g. "context includes
lifting_syntax begin ... end". Minor INCOMPATIBILITY.

* Code generation for scala: ambiguous implicts in class diagrams
are spelt out explicitly.

* Abstract locales semigroup, abel_semigroup, semilattice,
semilattice_neutr, ordering, ordering_top, semilattice_order,
semilattice_neutr_order, comm_monoid_set, semilattice_set,
semilattice_neutr_set, semilattice_order_set, semilattice_order_neutr_set
monoid_list, comm_monoid_list, comm_monoid_list_set, comm_monoid_mset,
comm_monoid_fun use boldified syntax uniformly that does not clash
with corresponding global syntax.  INCOMPATIBILITY.

* Conventional syntax "%(). t" for unit abstractions.  Slight syntactic
INCOMPATIBILITY.

* Command 'code_reflect' accepts empty constructor lists for datatypes,
which renders those abstract effectively.

* Command 'export_code' checks given constants for abstraction violations:
a small guarantee that given constants specify a safe interface for the
generated code.

* Probability/Random_Permutations.thy contains some theory about
choosing a permutation of a set uniformly at random and folding over a
list in random order.

* Probability/SPMF formalises discrete subprobability distributions.

* Library/FinFun.thy: bundles "finfun_syntax" and "no_finfun_syntax"
allow to control optional syntax in local contexts; this supersedes
former Library/FinFun_Syntax.thy. INCOMPATIBILITY, e.g. use "unbundle
finfun_syntax" to imitate import of "~~/src/HOL/Library/FinFun_Syntax".

* Library/Set_Permutations.thy (executably) defines the set of
permutations of a set, i.e. the set of all lists that contain every
element of the carrier set exactly once.

* Static evaluators (Code_Evaluation.static_* in Isabelle/ML) rely on
explicitly provided auxiliary definitions for required type class
dictionaries rather than half-working magic.  INCOMPATIBILITY, see
the tutorial on code generation for details.

* New abbreviations for negated existence (but not bounded existence):

  \<nexists>x. P x \<equiv> \<not> (\<exists>x. P x)
  \<nexists>!x. P x \<equiv> \<not> (\<exists>!x. P x)

* The print mode "HOL" for ASCII syntax of binders "!", "?", "?!", "@"
has been removed for output. It is retained for input only, until it is
eliminated altogether.

* metis: The problem encoding has changed very slightly. This might
break existing proofs. INCOMPATIBILITY.

* Sledgehammer:
  - The MaSh relevance filter is now faster than before.
  - Produce syntactically correct Vampire 4.0 problem files.

* The 'coinductive' command produces a proper coinduction rule for
mutual coinductive predicates. This new rule replaces the old rule,
which exposed details of the internal fixpoint construction and was
hard to use. INCOMPATIBILITY.

* (Co)datatype package:
  - New commands for defining corecursive functions and reasoning about
    them in "~~/src/HOL/Library/BNF_Corec.thy": 'corec', 'corecursive',
    'friend_of_corec', and 'corecursion_upto'; and 'corec_unique' proof
    method. See 'isabelle doc corec'.
  - The predicator :: ('a => bool) => 'a F => bool is now a first-class
    citizen in bounded natural functors.
  - 'primrec' now allows nested calls through the predicator in addition
    to the map function.
  - 'bnf' automatically discharges reflexive proof obligations.
  - 'bnf' outputs a slightly modified proof obligation expressing rel in
       terms of map and set
       (not giving a specification for rel makes this one reflexive).
  - 'bnf' outputs a new proof obligation expressing pred in terms of set
       (not giving a specification for pred makes this one reflexive).
    INCOMPATIBILITY: manual 'bnf' declarations may need adjustment.
  - Renamed lemmas:
      rel_prod_apply ~> rel_prod_inject
      pred_prod_apply ~> pred_prod_inject
    INCOMPATIBILITY.
  - The "size" plugin has been made compatible again with locales.
  - The theorems about "rel" and "set" may have a slightly different (but
    equivalent) form.
    INCOMPATIBILITY.

* Some old / obsolete theorems have been renamed / removed, potential
INCOMPATIBILITY.

  nat_less_cases  --  removed, use linorder_cases instead
  inv_image_comp  --  removed, use image_inv_f_f instead
  image_surj_f_inv_f  ~>  image_f_inv_f

* Some theorems about groups and orders have been generalised from
  groups to semi-groups that are also monoids:
    le_add_same_cancel1
    le_add_same_cancel2
    less_add_same_cancel1
    less_add_same_cancel2
    add_le_same_cancel1
    add_le_same_cancel2
    add_less_same_cancel1
    add_less_same_cancel2

* Some simplifications theorems about rings have been removed, since
  superseeded by a more general version:
    less_add_cancel_left_greater_zero ~> less_add_same_cancel1
    less_add_cancel_right_greater_zero ~> less_add_same_cancel2
    less_eq_add_cancel_left_greater_eq_zero ~> le_add_same_cancel1
    less_eq_add_cancel_right_greater_eq_zero ~> le_add_same_cancel2
    less_eq_add_cancel_left_less_eq_zero ~> add_le_same_cancel1
    less_eq_add_cancel_right_less_eq_zero ~> add_le_same_cancel2
    less_add_cancel_left_less_zero ~> add_less_same_cancel1
    less_add_cancel_right_less_zero ~> add_less_same_cancel2
INCOMPATIBILITY.

* Renamed split_if -> if_split and split_if_asm -> if_split_asm to
resemble the f.split naming convention, INCOMPATIBILITY.

* Characters (type char) are modelled as finite algebraic type
corresponding to {0..255}.

  - Logical representation:
    * 0 is instantiated to the ASCII zero character.
    * All other characters are represented as "Char n"
      with n being a raw numeral expression less than 256.
    * Expressions of the form "Char n" with n greater than 255
      are non-canonical.
  - Printing and parsing:
    * Printable characters are printed and parsed as "CHR ''\<dots>''"
      (as before).
    * The ASCII zero character is printed and parsed as "0".
    * All other canonical characters are printed as "CHR 0xXX"
      with XX being the hexadecimal character code.  "CHR n"
      is parsable for every numeral expression n.
    * Non-canonical characters have no special syntax and are
      printed as their logical representation.
  - Explicit conversions from and to the natural numbers are
    provided as char_of_nat, nat_of_char (as before).
  - The auxiliary nibble type has been discontinued.

INCOMPATIBILITY.

* Multiset membership is now expressed using set_mset rather than count.

  - Expressions "count M a > 0" and similar simplify to membership
    by default.

  - Converting between "count M a = 0" and non-membership happens using
    equations count_eq_zero_iff and not_in_iff.

  - Rules count_inI and in_countE obtain facts of the form
    "count M a = n" from membership.

  - Rules count_in_diffI and in_diff_countE obtain facts of the form
    "count M a = n + count N a" from membership on difference sets.

INCOMPATIBILITY.

* The names of multiset theorems have been normalised to distinguish which
  ordering the theorems are about
    mset_less_eqI ~> mset_subset_eqI
    mset_less_insertD ~> mset_subset_insertD
    mset_less_eq_count ~> mset_subset_eq_count
    mset_less_diff_self ~> mset_subset_diff_self
    mset_le_exists_conv ~> mset_subset_eq_exists_conv
    mset_le_mono_add_right_cancel ~> mset_subset_eq_mono_add_right_cancel
    mset_le_mono_add_left_cancel ~> mset_subset_eq_mono_add_left_cancel
    mset_le_mono_add ~> mset_subset_eq_mono_add
    mset_le_add_left ~> mset_subset_eq_add_left
    mset_le_add_right ~> mset_subset_eq_add_right
    mset_le_single ~> mset_subset_eq_single
    mset_le_multiset_union_diff_commute ~> mset_subset_eq_multiset_union_diff_commute
    diff_le_self ~> diff_subset_eq_self
    mset_leD ~> mset_subset_eqD
    mset_lessD ~> mset_subsetD
    mset_le_insertD ~> mset_subset_eq_insertD
    mset_less_of_empty ~> mset_subset_of_empty
    le_empty ~> subset_eq_empty
    mset_less_add_bothsides ~> mset_subset_add_bothsides
    mset_less_empty_nonempty ~> mset_subset_empty_nonempty
    mset_less_size ~> mset_subset_size
    wf_less_mset_rel ~> wf_subset_mset_rel
    count_le_replicate_mset_le ~> count_le_replicate_mset_subset_eq
    mset_remdups_le ~> mset_remdups_subset_eq
    ms_lesseq_impl ~> subset_eq_mset_impl

  Some functions have been renamed:
    ms_lesseq_impl -> subset_eq_mset_impl

* Multisets are now ordered with the multiset ordering
    #\<subseteq># ~> \<le>
    #\<subset># ~> <
    le_multiset ~> less_eq_multiset
    less_multiset ~> le_multiset
INCOMPATIBILITY.

* The prefix multiset_order has been discontinued: the theorems can be directly
accessed. As a consequence, the lemmas "order_multiset" and "linorder_multiset"
have been discontinued, and the interpretations "multiset_linorder" and
"multiset_wellorder" have been replaced by instantiations.
INCOMPATIBILITY.

* Some theorems about the multiset ordering have been renamed:
    le_multiset_def ~> less_eq_multiset_def
    less_multiset_def ~> le_multiset_def
    less_eq_imp_le_multiset ~> subset_eq_imp_le_multiset
    mult_less_not_refl ~> mset_le_not_refl
    mult_less_trans ~> mset_le_trans
    mult_less_not_sym ~> mset_le_not_sym
    mult_less_asym ~> mset_le_asym
    mult_less_irrefl ~> mset_le_irrefl
    union_less_mono2{,1,2} ~> union_le_mono2{,1,2}

    le_multiset\<^sub>H\<^sub>O ~> less_eq_multiset\<^sub>H\<^sub>O
    le_multiset_total ~> less_eq_multiset_total
    less_multiset_right_total ~> subset_eq_imp_le_multiset
    le_multiset_empty_left ~> less_eq_multiset_empty_left
    le_multiset_empty_right ~> less_eq_multiset_empty_right
    less_multiset_empty_right ~> le_multiset_empty_left
    less_multiset_empty_left ~> le_multiset_empty_right
    union_less_diff_plus ~> union_le_diff_plus
    ex_gt_count_imp_less_multiset ~> ex_gt_count_imp_le_multiset
    less_multiset_plus_left_nonempty ~> le_multiset_plus_left_nonempty
    le_multiset_plus_right_nonempty ~> le_multiset_plus_right_nonempty
    less_multiset_plus_plus_left_iff ~> le_multiset_plus_plus_left_iff
    less_multiset_plus_plus_right_iff ~> le_multiset_plus_plus_right_iff
INCOMPATIBILITY.

* The lemma mset_map has now the attribute [simp].
INCOMPATIBILITY.

* Some theorems about multisets have been removed:
    le_multiset_plus_plus_left_iff ~> add_less_cancel_right
    le_multiset_plus_plus_right_iff ~> add_less_cancel_left
    add_eq_self_empty_iff ~> add_cancel_left_right
    mset_subset_add_bothsides ~> subset_mset.add_less_cancel_right
INCOMPATIBILITY.

* Some typeclass constraints about multisets have been reduced from ordered or
linordered to preorder. Multisets have the additional typeclasses order_bot,
no_top, ordered_ab_semigroup_add_imp_le, ordered_cancel_comm_monoid_add,
linordered_cancel_ab_semigroup_add, and ordered_ab_semigroup_monoid_add_imp_le.
INCOMPATIBILITY.

* There are some new simplification rules about multisets, the multiset
ordering, and the subset ordering on multisets.
INCOMPATIBILITY.

* The subset ordering on multisets has now the interpretations
ordered_ab_semigroup_monoid_add_imp_le and bounded_lattice_bot.
INCOMPATIBILITY.

* Multiset: single has been removed in favor of add_mset that roughly
corresponds to Set.insert. Some theorems have removed or changed:
  single_not_empty ~> add_mset_not_empty or empty_not_add_mset
  fold_mset_insert ~> fold_mset_add_mset
  image_mset_insert ~> image_mset_add_mset
  union_single_eq_diff
  multi_self_add_other_not_self
  diff_single_eq_union
INCOMPATIBILITY.

* Multiset: some theorems have been changed to use add_mset instead of single:
  mset_add
  multi_self_add_other_not_self
  diff_single_eq_union
  union_single_eq_diff
  union_single_eq_member
  add_eq_conv_diff
  insert_noteq_member
  add_eq_conv_ex
  multi_member_split
  multiset_add_sub_el_shuffle
  mset_subset_eq_insertD
  mset_subset_insertD
  insert_subset_eq_iff
  insert_union_subset_iff
  multi_psub_of_add_self
  inter_add_left1
  inter_add_left2
  inter_add_right1
  inter_add_right2
  sup_union_left1
  sup_union_left2
  sup_union_right1
  sup_union_right2
  size_eq_Suc_imp_eq_union
  multi_nonempty_split
  mset_insort
  mset_update
  mult1I
  less_add
  mset_zip_take_Cons_drop_twice
  rel_mset_Zero
  msed_map_invL
  msed_map_invR
  msed_rel_invL
  msed_rel_invR
  le_multiset_right_total
  multiset_induct
  multiset_induct2_size
  multiset_induct2
INCOMPATIBILITY.

* Multiset: the definitions of some constants have changed to use add_mset instead
of adding a single element:
  image_mset
  mset
  replicate_mset
  mult1
  pred_mset
  rel_mset'
  mset_insort
INCOMPATIBILITY.

* Due to the above changes, the attributes of some multiset theorems have
been changed:
  insert_DiffM  [] ~> [simp]
  insert_DiffM2 [simp] ~> []
  diff_add_mset_swap [simp]
  fold_mset_add_mset [simp]
  diff_diff_add [simp] (for multisets only)
  diff_cancel [simp] ~> []
  count_single [simp] ~> []
  set_mset_single [simp] ~> []
  size_multiset_single [simp] ~> []
  size_single [simp] ~> []
  image_mset_single [simp] ~> []
  mset_subset_eq_mono_add_right_cancel [simp] ~> []
  mset_subset_eq_mono_add_left_cancel [simp] ~> []
  fold_mset_single [simp] ~> []
  subset_eq_empty [simp] ~> []
  empty_sup [simp] ~> []
  sup_empty [simp] ~> []
  inter_empty [simp] ~> []
  empty_inter [simp] ~> []
INCOMPATIBILITY.

* The order of the variables in the second cases of multiset_induct,
multiset_induct2_size, multiset_induct2 has been changed (e.g. Add A a ~> Add a A).
INCOMPATIBILITY.

* There is now a simplification procedure on multisets. It mimics the behavior
of the procedure on natural numbers.
INCOMPATIBILITY.

* Renamed sums and products of multisets:
  msetsum ~> sum_mset
  msetprod ~> prod_mset

* The symbols for intersection and union of multisets have been changed:
  #\<inter> ~> \<inter>#
  #\<union> ~> \<union>#
INCOMPATIBILITY.

* The lemma one_step_implies_mult_aux on multisets has been removed, use
one_step_implies_mult instead.
INCOMPATIBILITY.

* The following theorems have been renamed:
  setsum_left_distrib ~> setsum_distrib_right
  setsum_right_distrib ~> setsum_distrib_left
INCOMPATIBILITY.

* Compound constants INFIMUM and SUPREMUM are mere abbreviations now.
INCOMPATIBILITY.

* "Gcd (f ` A)" and "Lcm (f ` A)" are printed with optional
comprehension-like syntax analogously to "Inf (f ` A)" and "Sup (f ` A)".

* Class semiring_Lcd merged into semiring_Gcd.  INCOMPATIBILITY.

* The type class ordered_comm_monoid_add is now called
ordered_cancel_comm_monoid_add. A new type class ordered_comm_monoid_add is
introduced as the combination of ordered_ab_semigroup_add + comm_monoid_add.
INCOMPATIBILITY.

* Introduced the type classes canonically_ordered_comm_monoid_add and dioid.

* Introduced the type class ordered_ab_semigroup_monoid_add_imp_le. When
instantiating linordered_semiring_strict and ordered_ab_group_add, an explicit
instantiation of ordered_ab_semigroup_monoid_add_imp_le might be
required.
INCOMPATIBILITY.

* Added topological_monoid

* Library/Complete_Partial_Order2.thy provides reasoning support for
proofs about monotonicity and continuity in chain-complete partial
orders and about admissibility conditions for fixpoint inductions.

* Library/Polynomial.thy contains also derivation of polynomials
but not gcd/lcm on polynomials over fields.  This has been moved
to a separate theory Library/Polynomial_GCD_euclidean.thy, to
pave way for a possible future different type class instantiation
for polynomials over factorial rings.  INCOMPATIBILITY.

* Library/Sublist.thy: added function "prefixes" and renamed
  prefixeq -> prefix
  prefix -> strict_prefix
  suffixeq -> suffix
  suffix -> strict_suffix
  Added theory of longest common prefixes.

* Dropped various legacy fact bindings, whose replacements are often
of a more general type also:
  lcm_left_commute_nat ~> lcm.left_commute
  lcm_left_commute_int ~> lcm.left_commute
  gcd_left_commute_nat ~> gcd.left_commute
  gcd_left_commute_int ~> gcd.left_commute
  gcd_greatest_iff_nat ~> gcd_greatest_iff
  gcd_greatest_iff_int ~> gcd_greatest_iff
  coprime_dvd_mult_nat ~> coprime_dvd_mult
  coprime_dvd_mult_int ~> coprime_dvd_mult
  zpower_numeral_even ~> power_numeral_even
  gcd_mult_cancel_nat ~> gcd_mult_cancel
  gcd_mult_cancel_int ~> gcd_mult_cancel
  div_gcd_coprime_nat ~> div_gcd_coprime
  div_gcd_coprime_int ~> div_gcd_coprime
  zpower_numeral_odd ~> power_numeral_odd
  zero_less_int_conv ~> of_nat_0_less_iff
  gcd_greatest_nat ~> gcd_greatest
  gcd_greatest_int ~> gcd_greatest
  coprime_mult_nat ~> coprime_mult
  coprime_mult_int ~> coprime_mult
  lcm_commute_nat ~> lcm.commute
  lcm_commute_int ~> lcm.commute
  int_less_0_conv ~> of_nat_less_0_iff
  gcd_commute_nat ~> gcd.commute
  gcd_commute_int ~> gcd.commute
  Gcd_insert_nat ~> Gcd_insert
  Gcd_insert_int ~> Gcd_insert
  of_int_int_eq ~> of_int_of_nat_eq
  lcm_least_nat ~> lcm_least
  lcm_least_int ~> lcm_least
  lcm_assoc_nat ~> lcm.assoc
  lcm_assoc_int ~> lcm.assoc
  int_le_0_conv ~> of_nat_le_0_iff
  int_eq_0_conv ~> of_nat_eq_0_iff
  Gcd_empty_nat ~> Gcd_empty
  Gcd_empty_int ~> Gcd_empty
  gcd_assoc_nat ~> gcd.assoc
  gcd_assoc_int ~> gcd.assoc
  zero_zle_int ~> of_nat_0_le_iff
  lcm_dvd2_nat ~> dvd_lcm2
  lcm_dvd2_int ~> dvd_lcm2
  lcm_dvd1_nat ~> dvd_lcm1
  lcm_dvd1_int ~> dvd_lcm1
  gcd_zero_nat ~> gcd_eq_0_iff
  gcd_zero_int ~> gcd_eq_0_iff
  gcd_dvd2_nat ~> gcd_dvd2
  gcd_dvd2_int ~> gcd_dvd2
  gcd_dvd1_nat ~> gcd_dvd1
  gcd_dvd1_int ~> gcd_dvd1
  int_numeral ~> of_nat_numeral
  lcm_ac_nat ~> ac_simps
  lcm_ac_int ~> ac_simps
  gcd_ac_nat ~> ac_simps
  gcd_ac_int ~> ac_simps
  abs_int_eq ~> abs_of_nat
  zless_int ~> of_nat_less_iff
  zdiff_int ~> of_nat_diff
  zadd_int ~> of_nat_add
  int_mult ~> of_nat_mult
  int_Suc ~> of_nat_Suc
  inj_int ~> inj_of_nat
  int_1 ~> of_nat_1
  int_0 ~> of_nat_0
  Lcm_empty_nat ~> Lcm_empty
  Lcm_empty_int ~> Lcm_empty
  Lcm_insert_nat ~> Lcm_insert
  Lcm_insert_int ~> Lcm_insert
  comp_fun_idem_gcd_nat ~> comp_fun_idem_gcd
  comp_fun_idem_gcd_int ~> comp_fun_idem_gcd
  comp_fun_idem_lcm_nat ~> comp_fun_idem_lcm
  comp_fun_idem_lcm_int ~> comp_fun_idem_lcm
  Lcm_eq_0 ~> Lcm_eq_0_I
  Lcm0_iff ~> Lcm_0_iff
  Lcm_dvd_int ~> Lcm_least
  divides_mult_nat ~> divides_mult
  divides_mult_int ~> divides_mult
  lcm_0_nat ~> lcm_0_right
  lcm_0_int ~> lcm_0_right
  lcm_0_left_nat ~> lcm_0_left
  lcm_0_left_int ~> lcm_0_left
  dvd_gcd_D1_nat ~> dvd_gcdD1
  dvd_gcd_D1_int ~> dvd_gcdD1
  dvd_gcd_D2_nat ~> dvd_gcdD2
  dvd_gcd_D2_int ~> dvd_gcdD2
  coprime_dvd_mult_iff_nat ~> coprime_dvd_mult_iff
  coprime_dvd_mult_iff_int ~> coprime_dvd_mult_iff
  realpow_minus_mult ~> power_minus_mult
  realpow_Suc_le_self ~> power_Suc_le_self
  dvd_Gcd, dvd_Gcd_nat, dvd_Gcd_int removed in favour of Gcd_greatest
INCOMPATIBILITY.

* Session HOL-NSA has been renamed to HOL-Nonstandard_Analysis.

* Renamed HOL/Quotient_Examples/FSet.thy to
HOL/Quotient_Examples/Quotient_FSet.thy
INCOMPATIBILITY.

*** ML ***

* ML antiquotation @{path} is superseded by @{file}, which ensures that
the argument is a plain file. Minor INCOMPATIBILITY.

* Integer.gcd and Integer.lcm use efficient operations from the Poly/ML
library (notably for big integers). Subtle change of semantics:
Integer.gcd and Integer.lcm both normalize the sign, results are never
negative. This coincides with the definitions in HOL/GCD.thy.
INCOMPATIBILITY.

* Structure Rat for rational numbers is now an integral part of
Isabelle/ML, with special notation @int/nat or @int for numerals (an
abbreviation for antiquotation @{Pure.rat argument}) and ML pretty
printing. Standard operations on type Rat.rat are provided via ad-hoc
overloading of + - * / < <= > >= ~ abs. INCOMPATIBILITY, need to
use + instead of +/ etc. Moreover, exception Rat.DIVZERO has been
superseded by General.Div.

* The ML function "ML" provides easy access to run-time compilation.
This is particularly useful for conditional compilation, without
requiring separate files.

* Low-level ML system structures (like PolyML and RunCall) are no longer
exposed to Isabelle/ML user-space. Potential INCOMPATIBILITY.

* Antiquotation @{make_string} is available during Pure bootstrap --
with approximative output quality.

* Option ML_exception_debugger controls detailed exception trace via the
Poly/ML debugger. Relevant ML modules need to be compiled beforehand
with ML_file_debug, or with ML_file and option ML_debugger enabled. Note
debugger information requires consirable time and space: main
Isabelle/HOL with full debugger support may need ML_system_64.

* Local_Theory.restore has been renamed to Local_Theory.reset to
emphasize its disruptive impact on the cumulative context, notably the
scope of 'private' or 'qualified' names. Note that Local_Theory.reset is
only appropriate when targets are managed, e.g. starting from a global
theory and returning to it. Regular definitional packages should use
balanced blocks of Local_Theory.open_target versus
Local_Theory.close_target instead. Rare INCOMPATIBILITY.

* Structure TimeLimit (originally from the SML/NJ library) has been
replaced by structure Timeout, with slightly different signature.
INCOMPATIBILITY.

* Discontinued cd and pwd operations, which are not well-defined in a
multi-threaded environment. Note that files are usually located
relatively to the master directory of a theory (see also
File.full_path). Potential INCOMPATIBILITY.

* Binding.empty_atts supersedes Thm.empty_binding and
Attrib.empty_binding. Minor INCOMPATIBILITY.


*** System ***

* Many Isabelle tools that require a Java runtime system refer to the
settings ISABELLE_TOOL_JAVA_OPTIONS32 / ISABELLE_TOOL_JAVA_OPTIONS64,
depending on the underlying platform. The settings for "isabelle build"
ISABELLE_BUILD_JAVA_OPTIONS32 / ISABELLE_BUILD_JAVA_OPTIONS64 have been
discontinued. Potential INCOMPATIBILITY.

* The Isabelle system environment always ensures that the main
executables are found within the shell search $PATH: "isabelle" and
"isabelle_scala_script".

* Isabelle tools may consist of .scala files: the Scala compiler is
invoked on the spot. The source needs to define some object that extends
Isabelle_Tool.Body.

* The Isabelle ML process is now managed directly by Isabelle/Scala, and
shell scripts merely provide optional command-line access. In
particular:

  . Scala module ML_Process to connect to the raw ML process,
    with interaction via stdin/stdout/stderr or in batch mode;
  . command-line tool "isabelle console" as interactive wrapper;
  . command-line tool "isabelle process" as batch mode wrapper.

* The executable "isabelle_process" has been discontinued. Tools and
prover front-ends should use ML_Process or Isabelle_Process in
Isabelle/Scala. INCOMPATIBILITY.

* New command-line tool "isabelle process" supports ML evaluation of
literal expressions (option -e) or files (option -f) in the context of a
given heap image. Errors lead to premature exit of the ML process with
return code 1.

* Command-line tool "isabelle console" provides option -r to help to
bootstrapping Isabelle/Pure interactively.

* Command-line tool "isabelle yxml" has been discontinued.
INCOMPATIBILITY, use operations from the modules "XML" and "YXML" in
Isabelle/ML or Isabelle/Scala.

* File.bash_string, File.bash_path etc. represent Isabelle/ML and
Isabelle/Scala strings authentically within GNU bash. This is useful to
produce robust shell scripts under program control, without worrying
about spaces or special characters. Note that user output works via
Path.print (ML) or Path.toString (Scala). INCOMPATIBILITY, the old (and
less versatile) operations File.shell_quote, File.shell_path etc. have
been discontinued.

* SML/NJ and old versions of Poly/ML are no longer supported.

* Poly/ML heaps now follow the hierarchy of sessions, and thus require
much less disk space.

* System option "checkpoint" helps to fine-tune the global heap space
management of isabelle build. This is relevant for big sessions that may
exhaust the small 32-bit address space of the ML process (which is used
by default).



New in Isabelle2016 (February 2016)
-----------------------------------

*** General ***

* Eisbach is now based on Pure instead of HOL. Objects-logics may import
either the theory ~~/src/HOL/Eisbach/Eisbach (for HOL etc.) or
~~/src/HOL/Eisbach/Eisbach_Old_Appl_Syntax (for FOL, ZF etc.). Note that
the HOL-Eisbach session located in ~~/src/HOL/Eisbach/ contains further
examples that do require HOL.

* Better resource usage on all platforms (Linux, Windows, Mac OS X) for
both Isabelle/ML and Isabelle/Scala.  Slightly reduced heap space usage.

* Former "xsymbols" syntax with Isabelle symbols is used by default,
without any special print mode. Important ASCII replacement syntax
remains available under print mode "ASCII", but less important syntax
has been removed (see below).

* Support for more arrow symbols, with rendering in LaTeX and Isabelle
fonts: \<Lleftarrow> \<Rrightarrow> \<longlongleftarrow> \<longlongrightarrow> \<longlonglongleftarrow> \<longlonglongrightarrow>.

* Special notation \<struct> for the first implicit 'structure' in the
context has been discontinued. Rare INCOMPATIBILITY, use explicit
structure name instead, notably in indexed notation with block-subscript
(e.g. \<odot>\<^bsub>A\<^esub>).

* The glyph for \<diamond> in the IsabelleText font now corresponds better to its
counterpart \<box> as quantifier-like symbol. A small diamond is available as
\<diamondop>; the old symbol \<struct> loses this rendering and any special
meaning.

* Syntax for formal comments "-- text" now also supports the symbolic
form "\<comment> text". Command-line tool "isabelle update_cartouches -c" helps
to update old sources.

* Toplevel theorem statements have been simplified as follows:

  theorems             ~>  lemmas
  schematic_lemma      ~>  schematic_goal
  schematic_theorem    ~>  schematic_goal
  schematic_corollary  ~>  schematic_goal

Command-line tool "isabelle update_theorems" updates theory sources
accordingly.

* Toplevel theorem statement 'proposition' is another alias for
'theorem'.

* The old 'defs' command has been removed (legacy since Isabelle2014).
INCOMPATIBILITY, use regular 'definition' instead. Overloaded and/or
deferred definitions require a surrounding 'overloading' block.


*** Prover IDE -- Isabelle/Scala/jEdit ***

* IDE support for the source-level debugger of Poly/ML, to work with
Isabelle/ML and official Standard ML. Option "ML_debugger" and commands
'ML_file_debug', 'ML_file_no_debug', 'SML_file_debug',
'SML_file_no_debug' control compilation of sources with or without
debugging information. The Debugger panel allows to set breakpoints (via
context menu), step through stopped threads, evaluate local ML
expressions etc. At least one Debugger view needs to be active to have
any effect on the running ML program.

* The State panel manages explicit proof state output, with dynamic
auto-update according to cursor movement. Alternatively, the jEdit
action "isabelle.update-state" (shortcut S+ENTER) triggers manual
update.

* The Output panel no longer shows proof state output by default, to
avoid GUI overcrowding. INCOMPATIBILITY, use the State panel instead or
enable option "editor_output_state".

* The text overview column (status of errors, warnings etc.) is updated
asynchronously, leading to much better editor reactivity. Moreover, the
full document node content is taken into account. The width of the
column is scaled according to the main text area font, for improved
visibility.

* The main text area no longer changes its color hue in outdated
situations. The text overview column takes over the role to indicate
unfinished edits in the PIDE pipeline. This avoids flashing text display
due to ad-hoc updates by auxiliary GUI components, such as the State
panel.

* Slightly improved scheduling for urgent print tasks (e.g. command
state output, interactive queries) wrt. long-running background tasks.

* Completion of symbols via prefix of \<name> or \<^name> or \name is
always possible, independently of the language context. It is never
implicit: a popup will show up unconditionally.

* Additional abbreviations for syntactic completion may be specified in
$ISABELLE_HOME/etc/abbrevs and $ISABELLE_HOME_USER/etc/abbrevs, with
support for simple templates using ASCII 007 (bell) as placeholder.

* Symbols \<oplus>, \<Oplus>, \<otimes>, \<Otimes>, \<odot>, \<Odot>, \<ominus>, \<oslash> no longer provide abbreviations for
completion like "+o", "*o", ".o" etc. -- due to conflicts with other
ASCII syntax. INCOMPATIBILITY, use plain backslash-completion or define
suitable abbreviations in $ISABELLE_HOME_USER/etc/abbrevs.

* Action "isabelle-emph" (with keyboard shortcut C+e LEFT) controls
emphasized text style; the effect is visible in document output, not in
the editor.

* Action "isabelle-reset" now uses keyboard shortcut C+e BACK_SPACE,
instead of former C+e LEFT.

* The command-line tool "isabelle jedit" and the isabelle.Main
application wrapper treat the default $USER_HOME/Scratch.thy more
uniformly, and allow the dummy file argument ":" to open an empty buffer
instead.

* New command-line tool "isabelle jedit_client" allows to connect to an
already running Isabelle/jEdit process. This achieves the effect of
single-instance applications seen on common GUI desktops.

* The default look-and-feel for Linux is the traditional "Metal", which
works better with GUI scaling for very high-resolution displays (e.g.
4K). Moreover, it is generally more robust than "Nimbus".

* Update to jedit-5.3.0, with improved GUI scaling and support of
high-resolution displays (e.g. 4K).

* The main Isabelle executable is managed as single-instance Desktop
application uniformly on all platforms: Linux, Windows, Mac OS X.


*** Document preparation ***

* Text and ML antiquotation @{locale} for locales, similar to existing
antiquotations for classes.

* Commands 'paragraph' and 'subparagraph' provide additional section
headings. Thus there are 6 levels of standard headings, as in HTML.

* Command 'text_raw' has been clarified: input text is processed as in
'text' (with antiquotations and control symbols). The key difference is
the lack of the surrounding isabelle markup environment in output.

* Text is structured in paragraphs and nested lists, using notation that
is similar to Markdown. The control symbols for list items are as
follows:

  \<^item>  itemize
  \<^enum>  enumerate
  \<^descr>  description

* There is a new short form for antiquotations with a single argument
that is a cartouche: \<^name>\<open>...\<close> is equivalent to @{name \<open>...\<close>} and
\<open>...\<close> without control symbol is equivalent to @{cartouche \<open>...\<close>}.
\<^name> without following cartouche is equivalent to @{name}. The
standard Isabelle fonts provide glyphs to render important control
symbols, e.g. "\<^verbatim>", "\<^emph>", "\<^bold>".

* Antiquotations @{noindent}, @{smallskip}, @{medskip}, @{bigskip} with
corresponding control symbols \<^noindent>, \<^smallskip>, \<^medskip>, \<^bigskip> specify spacing formally, using
standard LaTeX macros of the same names.

* Antiquotation @{cartouche} in Isabelle/Pure is the same as @{text}.
Consequently, \<open>...\<close> without any decoration prints literal quasi-formal
text. Command-line tool "isabelle update_cartouches -t" helps to update
old sources, by approximative patching of the content of string and
cartouche tokens seen in theory sources.

* The @{text} antiquotation now ignores the antiquotation option
"source". The given text content is output unconditionally, without any
surrounding quotes etc. Subtle INCOMPATIBILITY, put quotes into the
argument where they are really intended, e.g. @{text \<open>"foo"\<close>}. Initial
or terminal spaces are ignored.

* Antiquotations @{emph} and @{bold} output LaTeX source recursively,
adding appropriate text style markup. These may be used in the short
form \<^emph>\<open>...\<close> and \<^bold>\<open>...\<close>.

* Document antiquotation @{footnote} outputs LaTeX source recursively,
marked as \footnote{}. This may be used in the short form \<^footnote>\<open>...\<close>.

* Antiquotation @{verbatim [display]} supports option "indent".

* Antiquotation @{theory_text} prints uninterpreted theory source text
(Isar outer syntax with command keywords etc.). This may be used in the
short form \<^theory_text>\<open>...\<close>. @{theory_text [display]} supports option "indent".

* Antiquotation @{doc ENTRY} provides a reference to the given
documentation, with a hyperlink in the Prover IDE.

* Antiquotations @{command}, @{method}, @{attribute} print checked
entities of the Isar language.

* HTML presentation uses the standard IsabelleText font and Unicode
rendering of Isabelle symbols like Isabelle/Scala/jEdit.  The former
print mode "HTML" loses its special meaning.


*** Isar ***

* Local goals ('have', 'show', 'hence', 'thus') allow structured rule
statements like fixes/assumes/shows in theorem specifications, but the
notation is postfix with keywords 'if' (or 'when') and 'for'. For
example:

  have result: "C x y"
    if "A x" and "B y"
    for x :: 'a and y :: 'a
    <proof>

The local assumptions are bound to the name "that". The result is
exported from context of the statement as usual. The above roughly
corresponds to a raw proof block like this:

  {
    fix x :: 'a and y :: 'a
    assume that: "A x" "B y"
    have "C x y" <proof>
  }
  note result = this

The keyword 'when' may be used instead of 'if', to indicate 'presume'
instead of 'assume' above.

* Assumptions ('assume', 'presume') allow structured rule statements
using 'if' and 'for', similar to 'have' etc. above. For example:

  assume result: "C x y"
    if "A x" and "B y"
    for x :: 'a and y :: 'a

This assumes "\<And>x y::'a. A x \<Longrightarrow> B y \<Longrightarrow> C x y" and produces a general
result as usual: "A ?x \<Longrightarrow> B ?y \<Longrightarrow> C ?x ?y".

Vacuous quantification in assumptions is omitted, i.e. a for-context
only effects propositions according to actual use of variables. For
example:

  assume "A x" and "B y" for x and y

is equivalent to:

  assume "\<And>x. A x" and "\<And>y. B y"

* The meaning of 'show' with Pure rule statements has changed: premises
are treated in the sense of 'assume', instead of 'presume'. This means,
a goal like "\<And>x. A x \<Longrightarrow> B x \<Longrightarrow> C x" can be solved completely as
follows:

  show "\<And>x. A x \<Longrightarrow> B x \<Longrightarrow> C x"

or:

  show "C x" if "A x" "B x" for x

Rare INCOMPATIBILITY, the old behaviour may be recovered as follows:

  show "C x" when "A x" "B x" for x

* New command 'consider' states rules for generalized elimination and
case splitting. This is like a toplevel statement "theorem obtains" used
within a proof body; or like a multi-branch 'obtain' without activation
of the local context elements yet.

* Proof method "cases" allows to specify the rule as first entry of
chained facts.  This is particularly useful with 'consider':

  consider (a) A | (b) B | (c) C <proof>
  then have something
  proof cases
    case a
    then show ?thesis <proof>
  next
    case b
    then show ?thesis <proof>
  next
    case c
    then show ?thesis <proof>
  qed

* Command 'case' allows fact name and attribute specification like this:

  case a: (c xs)
  case a [attributes]: (c xs)

Facts that are introduced by invoking the case context are uniformly
qualified by "a"; the same name is used for the cumulative fact. The old
form "case (c xs) [attributes]" is no longer supported. Rare
INCOMPATIBILITY, need to adapt uses of case facts in exotic situations,
and always put attributes in front.

* The standard proof method of commands 'proof' and '..' is now called
"standard" to make semantically clear what it is; the old name "default"
is still available as legacy for some time. Documentation now explains
'..' more accurately as "by standard" instead of "by rule".

* Nesting of Isar goal structure has been clarified: the context after
the initial backwards refinement is retained for the whole proof, within
all its context sections (as indicated via 'next'). This is e.g.
relevant for 'using', 'including', 'supply':

  have "A \<and> A" if a: A for A
    supply [simp] = a
  proof
    show A by simp
  next
    show A by simp
  qed

* Command 'obtain' binds term abbreviations (via 'is' patterns) in the
proof body as well, abstracted over relevant parameters.

* Improved type-inference for theorem statement 'obtains': separate
parameter scope for of each clause.

* Term abbreviations via 'is' patterns also work for schematic
statements: result is abstracted over unknowns.

* Command 'subgoal' allows to impose some structure on backward
refinements, to avoid proof scripts degenerating into long of 'apply'
sequences. Further explanations and examples are given in the isar-ref
manual.

* Command 'supply' supports fact definitions during goal refinement
('apply' scripts).

* Proof method "goal_cases" turns the current subgoals into cases within
the context; the conclusion is bound to variable ?case in each case. For
example:

lemma "\<And>x. A x \<Longrightarrow> B x \<Longrightarrow> C x"
  and "\<And>y z. U y \<Longrightarrow> V z \<Longrightarrow> W y z"
proof goal_cases
  case (1 x)
  then show ?case using \<open>A x\<close> \<open>B x\<close> sorry
next
  case (2 y z)
  then show ?case using \<open>U y\<close> \<open>V z\<close> sorry
qed

lemma "\<And>x. A x \<Longrightarrow> B x \<Longrightarrow> C x"
  and "\<And>y z. U y \<Longrightarrow> V z \<Longrightarrow> W y z"
proof goal_cases
  case prems: 1
  then show ?case using prems sorry
next
  case prems: 2
  then show ?case using prems sorry
qed

* The undocumented feature of implicit cases goal1, goal2, goal3, etc.
is marked as legacy, and will be removed eventually. The proof method
"goals" achieves a similar effect within regular Isar; often it can be
done more adequately by other means (e.g. 'consider').

* The vacuous fact "TERM x" may be established "by fact" or as `TERM x`
as well, not just "by this" or "." as before.

* Method "sleep" succeeds after a real-time delay (in seconds). This is
occasionally useful for demonstration and testing purposes.


*** Pure ***

* Qualifiers in locale expressions default to mandatory ('!') regardless
of the command. Previously, for 'locale' and 'sublocale' the default was
optional ('?'). The old synatx '!' has been discontinued.
INCOMPATIBILITY, remove '!' and add '?' as required.

* Keyword 'rewrites' identifies rewrite morphisms in interpretation
commands. Previously, the keyword was 'where'. INCOMPATIBILITY.

* More gentle suppression of syntax along locale morphisms while
printing terms. Previously 'abbreviation' and 'notation' declarations
would be suppressed for morphisms except term identity. Now
'abbreviation' is also kept for morphims that only change the involved
parameters, and only 'notation' is suppressed. This can be of great help
when working with complex locale hierarchies, because proof states are
displayed much more succinctly. It also means that only notation needs
to be redeclared if desired, as illustrated by this example:

  locale struct = fixes composition :: "'a => 'a => 'a" (infixl "\<cdot>" 65)
  begin
    definition derived (infixl "\<odot>" 65) where ...
  end

  locale morphism =
    left: struct composition + right: struct composition'
    for composition (infix "\<cdot>" 65) and composition' (infix "\<cdot>''" 65)
  begin
    notation right.derived ("\<odot>''")
  end

* Command 'global_interpretation' issues interpretations into global
theories, with optional rewrite definitions following keyword 'defines'.

* Command 'sublocale' accepts optional rewrite definitions after keyword
'defines'.

* Command 'permanent_interpretation' has been discontinued. Use
'global_interpretation' or 'sublocale' instead. INCOMPATIBILITY.

* Command 'print_definitions' prints dependencies of definitional
specifications. This functionality used to be part of 'print_theory'.

* Configuration option rule_insts_schematic has been discontinued
(intermediate legacy feature in Isabelle2015). INCOMPATIBILITY.